Potential basement insulation issue

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flux84

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Just a bit of background before I get into the potential issue. I live fairly far north and have a basement with concrete foundation walls (not block). In the winter, we can get air temps as low as -35C or so. The house was built in 1999, and the basement is currently framed, insulated and vapor barriered - it has been like that for at least 7 years, and more than likely for 16 years. Metal framing, R12 fiberglass insulation.

On to the potential problem. I am looking to actually finish the basement, and was curious if the builder had put any rigid foam against the foundation, or if they just left an air gap. The vapor barrier wasn't sealed to the bottom plate - it was just draped and hung there, so lifting it up to look behind the insulation wasn't difficult. Turns out it was just an air gap, but the concrete itself looked like it had quiet a lot of block mold on it. The insulation seemed dry and free of mold.

I suspect that the concrete has mold due to condensation from the warmer basement air getting underneath the vapor barrier. What I don't entirely understand is why the insulation wasn't damp and moldy as well.

Does it make sense that the concrete is moldy and the insulation isn't, given what I described above? Or is there something else going on?

If it is mold, I intend to have anything removed and cleaned properly and am thinking that this would be what I'd do, in order from foundation wall outwards. 2 inch rigid foam (glued w/ PL300), bluwood or pinkwood framing (w/ sill gaskets against concrete), and roxul comfortbatt insulation (R14), vapor barrier, 5/8" drywall. Also debating 2 inch Roxul Comfortboard IS instead of the foam. Does that all make sense?

I appreciate any insight, advice or suggestions - I've only been researching proper basement insulation/building envelope type stuff recently when I decided to finish my basement...
 
Welcome to the site. Mold does not grow on concrete, but it will go on the dust if the moisture is there. Does the insulation give you proof of air movement, (dirty insulation).
 
Thanks!

The insulation seems mostly clean - I didn't really disturb it much to look at the back however. The front side looks clean though. I've attached a couple of photos of what I saw when I looked. Disregard the carpet color :)

IMG_4047.JPG

IMG_4048.JPG
 
Ya that dosn't look good. You might want get that tested before you open it up. The proble with this system is it is a closed area and insulation should have ventalation, just like an attic or crawlspace and that is usually missed. Foam against the concrete is likely a better bet. If you do a layer of foam, tape the joints and that is a vapour barrier, you don't want another after that.
 
Looks like the adhesive they use to adhere the fiberglass insulation to the kraft paper of faced insulation. Check to see if it's just paper against the concrete.
 
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